The present invention relates generally to a microscope and to a method of using that device and relates more particularly to an improved acoustic microscope which is capable of real time processing and to methods of using that device.
Today, there is much interest in acoustic microscopy. Using the methods and apparatus which have existed in the prior art, one can observe living cells; and no staining is required.
There are three known types of prior art acoustic microscopes, all of which use piezoelectric transducers. These three types are reflection acoustic microscopes (as disclosed in C. F. Quate, "The Acoustic Microscope," Sci. Am. 241, p. 62 (1979)), transmission acoustic microscopes, and scanning laser acoustic microscopes (SLAM's) (as disclosed in L. W. Kessler er al., "Principles and Analytical Capabilities of the Scanning Laser Acoustic Microscope (SLAM)," Scanning Electron Microscopy/1978/1, An International Review of Advances in Instrumentation Techniques, Theory, and Physical Applications of the Scanning Electron Microscope, Om Johari, Ed., SEM Inc., AMF O'Hare, Il., pp. 555-560. Reflection and transmission acoustic microscopes operate at very high frequencies (within the 1 to 3 gigahertz range) and thus give very good resolution which is comparable to that obtainable with optical microscopes. Both reflection and transmission acoustic microscopes have a focus which is produced by polishing a hemisphere into a material such as sapphire. However, both types require that the object plane move; and the object plane has had to be mechanically moved in order to scan the object. However, if high resolution is desired, one cannot move the object quickly because distortion results as the coupling fluid is disturbed by the motion. Therefore, any mechanical scanning that is done of necessity is very slow. Furthermore, real time processing (i.e., processing in which a specimen can be viewed while it is being scanned) has not been possible with these methods because each image must be stored and the data then later reassembled. Therefore, it has not been possible to view moving objects with these two types of acoustic microscopes.
With the third type of acoustic microscope, the scanning laser acoustic microscope, it has not been necessary to move the object; instead, a laser scans across the acoustic field which passes through a specimen. However, a disadvantage of this type of apparatus is that the frequencies employed of necessity have had to be quite low (on the order of 100 megahertz). Thus, the resolution obtainable has been poor. Additionally, like the two types of acoustic microscopes described above, planar samples are required in the SLAM. All three types require water or some other coupling medium, which introduces loss of signal and wetting of the samples.
Therefore, despite the acoustic microscopes which have existed in the prior art, a need has existed for an acoustic microscope which has simultaneously the advantages of good resolution, no requirement for planar samples, direct coupling to the specimen, and a capability of real time processing (so that the sample can be observed while it is being scanned).